Improved methods for the isolation and purification of porcine islets

Recent progress in human islet transplantation demonstrates the feasibility of using purified human islets for treatment of type 1 diabetes mellitus; however, a shortage of human pancreata remains a major obstacle. This report describes methods to isolate porcine islets using a modification of the automated chamber method. The pancreata from 2-year-old sows were trimmed and injected intraductally with Sevac, Sigma, or Liberase PI collagenase. The pancreata was placed in the chamber, shaken, and recirculated at 70 ml/min until an adequate number of islets were liberated. The digest was centrifuged and the pellets pooled with University of Wisconsin Solution + 10% horse serum and incubated at 4 degrees C for 1 h. The islets were purified using a continuous gradient of Hypaque Euroficoll on a refrigerated COBE 2991. The islets were collected in fractions, assessed for purity, sized, and then suspended in Medium 199. Collagenase preparations obtained from Sevac (2919 islet equivalents [IE]/g), Sigma (2543 IE/g), and Liberase PI (2901 IE/g) gave similar results with 94%-95% purity. In summary, we report a successful method for efficient isolation and purification of porcine islets, yielding nearly 3000 IE/gm, with different collagenase products.

Improved method for the isolation and purification of human islets of langerhans using Liberase enzyme blend

To determine the effects of procedural modifications, 23 human islet isolations were analyzed. Isolations were divided into two groups based on the enzyme used. The influence of Liberase, with an improved method of mechanical disassociation of pancreas, was compared to an automated method using Sevac collagenase. Pancreases were processed within 10 h of cross clamping. Following ductal injection of the enzyme, tissue was placed in the digestion chamber for disassociation. Purification was accomplished using a COBE 2991 cell processor and continuous gradients of 1Hypaque EuroFicoll. Isolations in Group I (Sevac) had an average yield of 138,602 +/- 128,364 islet equivalents (IE) (2083 +/- 1679 IE/g) with a purity of 85 +/- 11%. Group II (Liberase) showed an average yield of 389,586 +/- 191,161 IE (5,958 +/- 3,083 IE/g) with a purity of 90 +/- 6.8%. Viability was confirmed by fluorescein diacetate and propidium iodide staining, static incubations, and perifusions. In conclusion, the combination of the enzyme blend, Liberase, and a more gentle system of disassociation has proven to be a more productive method of islet isolation with higher purity than the previously published methods.

Prolonged survival of discordant porcine islet xenografts

Purified porcine islets were prepared by collagenase digestion and density gradient purification, and transplanted under the kidney capsule of C57B/B6 mice with streptozotocin-induced diabetes which were receiving varying temporary immunosuppressive therapies. Islets that had been cultured for 1 day at 37 degree C were rejected after : 9+/-0.1 (mean+/-SE) days in control mice: 14+/-3 days in mice receiving mouse antilymphocyte serum (MLS) plus porcine antilymphocyte serum (PLS) on day of transplant (day 0); 43+/-6 days in mice treated for 1 week with anti-CD4 antibody (aCD4); 36+/-4 days in mice given aCD4 for 1 week plus PLS on days 0 and 7; 47+/-3 days in mice treated with aCD4 for 1 week plus MLS and PLS on day 21. Porcine islet survival in these latter three groups was significantly (P<0.01) and similarly longer than in the control and MLS plus PLS groups. Then, we transplanted islets that had been either cultured at 24 degrees C for 7 days or cryopreserved into 7-day aCD4-treated mice, to evaluate whether low temperature culture or the freezing-thawing procedure could affect survival. Neither 7-day, low temperature culture (mean survival time: 37+/-2 days) nor cryopreservation (mean survival time: 39+/-2 days) prolonged islets function further. Thus, the present study demonstrates that prolonged survival can be achieved with discordant porcine islet xenografts, and shows the greater efficacy of aCD4 treatment, which was not improved by additional immunosuppressive therapies we tested, nor by culture or cryopreservation of the islets.

Continued insulin dependence despite normal range insulin sensitivity and insulin connecting peptide levels in a kidney/islet transplant patient

OBJECTIVE

The majority of islet transplant recipients remain insulin-requiring, although many have near-normal connecting peptide (CP) levels. Insulin resistance may be one possible cause of the continuing need for exogenous insulin in islet transplant recipients. To assess this, we have studied the insulin sensitivity index (S1) in one patient with near-normal CP levels after islet transplant who remained insulin-requiring.

RESEARCH DESIGN AND METHODS

The islet transplant recipient is a 36-year-old woman with no residual CP who received a kidney transplant, followed 7 days later by an islet transplant. The islets were infused into the liver via the umbilical vein. Induction immunosuppression consisted of OKT3, prednisone, cyclosporin A, and azathioprine, with maintenance on the latter three.

RESULTS

Maximum CP levels after a standardized Sustacal meal were 2.09, 1.18, 0.85, and 0.81 nmol/l at 1,6,18, and 24 months posttransplant, respectively. Insulin requirements at the same times were 0.27, 0.45, 0.49, and 0.62 U.kg(-1).d(-1), while S1 was 36.3, 53.3, and 13.2 min (-1).nmol(-1).ml at 6,18, and 24 months, respectively. This compares with S1 values of 43.3+/- 10.0 min (-1).nmol(-1).ml for normal subjects.

CONCLUSIONS

This patient had near-normal S1 and CP levels, but she was unable to discontinue insulin therapy, suggesting that other factors are critical. Despite this, she maintained normal or near-normal glycated hemoglobins, indicating metabolic benefit from the islet transplant.

Effect of cyclosporin treatment on metabolic and hormonal responses to mixed meal plus oral glucose in dogs with intrasplenic pancreatic islet autograft

We evaluated the effect of immunosuppressive concentrations of cyclosporin A (CsA), given intramuscularly, on the levels of glucose, insulin, C-peptide, glucagon, pancreatic polypeptide (PP), lactate, alanine and beta-hydroxy-butyrate in a group of pancreatectomized mongrel dogs with intrasplenic islet autografts, given mixed meal and oral glucose, while on or off CsA therapy. In whole blood, HPLC-measured drug levels ranged from 412 to 803 ng/ml. Basal glucose and insulin concentrations did not differ significantly between non-pancreatectomized, control dogs and transplanted animals, whether on or off CsA. After the meal challenge, glucose levels were significantly higher in transplanted animals than in normal dogs, and no additional deleterious effect of CsA was observed. Similar insulin and C-peptide responses were found in animals either on or off CsA treatment. Fasting and post-meal concentrations of glucagon, PP and intermediate metabolites were not affected by the drug. These results suggest that intramuscular CsA, given at doses known to sustain islet allograft function, has no detrimental effect on the hormonal and metabolic responses to mixed meal and oral glucose in dogs with intrasplenic islet autografts.

Protection of encapsulated human islets implanted without immunosuppression in patients with type I or type II diabetes and in nondiabetic control subjects

Human islets were macroencapsulated in permselective hollow fiber membrane devices and successfully allotransplanted subcutaneously with > 90% viability after 2 weeks in situ. Recipients were patients with type I or type II diabetes and normal control subjects; none was immunosuppressed. Between 150 and 200 islet equivalents were implanted in each of the nine patients. No adverse patient complications were observed. Biocompatibility of devices was excellent. Insulin-positive beta-cells were confirmed in encapsulated islets recovered from the implanted devices in all patient populations including the type I diabetic patients. Glucose-stimulated insulin release could be demonstrated in vitro from recovered islets. These data demonstrate that macroencapsulated human islets can survive at the subcutaneous site and that permselective membranes can be designed to protect against both allogeneic immune responses as well as the autoimmune component of type I diabetes.

Cryogenic storage of isolated, purified porcine pancreatic islets

Highly purified islets of Langerhans were prepared in the present study from adult pigs by collagenase digestion and density gradient purification. After overnight culture, the tissue was equilibrated with DMSO at 25 degrees C, supercooled to -7.5 degrees C, nucleated, slowly cooled at 0.25 degrees C/min to -40 degrees C, and stored at -130 degrees C. Then, after variable periods of storage, the islets were rapidly thawed at 37 degrees C. Postthaw actual islet and islet equivalent (150-microns sized islets) recovery were 75 +/- 7% and 66 +/- 4%, respectively. The frozen-thawed porcine islets maintained good morphology on histological staining by hematoxylin-eosin and aldehyde-fuchsin. Upon perifusion, basal insulin secretion was 43 +/- 10 and 67 +/- 18 pmol/L from noncryopreserved, control islets, and cryopreserved islets, respectively (P = 0.2). Peak insulin release at 16.7 mmol/L glucose was 85 +/- 28 pmol/L from noncryopreserved islets and 157 +/- 48 pmol/L from the frozen-thawed islets (P = 0.1). When 10 mmol/L theophylline was added to 16.7 mmol/L glucose, the secretion of the hormone peaked to 221 +/- 83 (control islets) and 479 +/- 140 pmol/L (cryopreserved islets, P = 0.1). Total insulin secretion differed significantly for the noncryopreserved and the cryopreserved islets at both 16.7 mmol/L (1412 +/- 306 vs. 3756 +/- 764 pmol/L, respectively, P = 0.007) and 16.7 mmol/L glucose plus 10 mmol/L theophylline (2161 +/- 371 vs. 7505 +/- 2075 pmol/L, respectively, P = 0.011). Normoglycemia was restored within 7 days from implantation in temporarily immunosuppressed (aL3T4 antibody) mice with streptozotocin-induced diabetes by transplanting 1500-2000 cryopreserved porcine islets under the kidney capsule. Mean survival time of frozen-thawed islet xenografts (39 +/- 3 days) was similar to that of noncryopreserved islet xenografts (43 +/- 6 days). This study demonstrates that cryogenic storage is feasible of isolated porcine islets, with the frozen-thawed pancreatic endocrine tissue maintaining morphological integrity and both in vitro and in vivo viability. Further studies are needed to define the effect of cryopreservation on the immunogenic properties of porcine islets.

Effects of cyclosporine on insulin secretion and insulin sensitivity in dogs with intrasplenic islet autotransplants

Concern about cyclosporine causing adverse effects on glucose metabolism is based mainly on in vitro studies and in vivo data in rodents. However, data on large mammals and humans are much more controversial. Because the drug is used as therapy accompanying pancreatic or isolated islet transplantations, studies in large animals are needed to assess whether cyclosporine inhibits beta-cell function and causes glucose intolerance. To address these issues, we examined intravenous glucose tolerance, islet beta-cell function, and insulin sensitivity in a group of adult mongrel dogs with intrasplenic islet autografts, with and without cyclosporine treatment. Similar fasting plasma glucose and insulin values were found before and after pancreatectomy and islet transplantation. After intravenous glucose, plasma glucose values decreased more slowly in dogs that had undergone transplantation, but no additional adverse effect as a result of cyclosporine was observed. During euglycemic clamp studies, performed at both physiologic and pharmacologic insulin concentrations, the drug had no effect on the total amount of metabolized glucose, and glucose production was unaffected by cyclosporine treatment. Thus intramuscular cyclosporine therapy does not seem to inhibit insulin secretion from heterotopic islets or to affect peripheral and hepatic insulin sensitivity in dogs with intrasplenic islet autografts.

The effect of pancreatic islet transplantation and insulin therapy on neuroaxonal dystrophy in sympathetic autonomic ganglia of chronic streptozocin-diabetic rats

The frequency of neuroaxonal dystrophy was determined in the superior mesenteric/celiac sympathetic ganglia in a streptozocin-treated rat model of diabetic autonomic neuropathy. Dystrophic axonopathy was increased 5- to 6-fold in 9-month untreated diabetics compared to age-matched controls. Pancreatic islet transplantation therapy or daily insulin administration prevented the development of dystrophic axonopathy. Transplantation of islets after 6 months of diabetes, a time at which dystrophic axonopathy is well developed, resulted in nearly complete resolution of the neuropathy within 3 months.

Automated method for isolation of human pancreatic islets

We describe an automated method for the isolation of human pancreatic islets. The procedure meets the following requirements: 1) minimal traumatic action on the islets, 2) continuous digestion in which the islets that are progressively liberated can be saved from further enzymatic action, 3) minimal human intervention in the digestion process, and 4) high yield and purity of the isolated islets. After purification on Ficoll gradients, an average of 164,600 islets/pancreas was obtained (2279 islets/g), with an average purity of 78.5% islets. The average volume and average insulin content of the final islet preparation were 348 mm3 and 93.4 U, respectively. The islets were morphologically intact with a normal degree of beta-granulation and responded to glucose stimulation with a fivefold increase of insulin secretion over basal levels. The procedure is now being used for the initiation of the second phase of clinical trials on human islet transplants.

The effect of pancreatic islet transplantation and insulin therapy on experimental diabetic autonomic neuropathy

Rats with chronic streptozotocin (SZ) diabetes develop dilatation of the alimentary tract, loss of fecal consistency, and autonomic neuropathy involving unmyelinated axons of the extrinsic innervation of the small bowel. Diabetic autonomic neuropathy involving the ileal mesenteric nerves is characterized by modest to marked dilatation of axons by distinctive subcellular organelles identical to those described in experimental and clinical axonal dystrophies. Axonopathy is confined to the alimentary tract; examination of myelinated and unmyelinated axons of the sciatic (midthigh level) and distal somatic nerves of the tail of diabetic animals with prominent ileal axonopathy failed to demonstrate significant numbers of dystrophic axons. The prevention or reversal of diabetic autonomic neuropathy by a variety of experimental manipulations clearly indicates that the lesions we have demonstrated in chronically SZ-induced diabetic animals were produced by diabetes and were not the result of a direct neurotoxic effect of the diabetogenic agent streptozotocin. Animals did not develop axonopathy after simultaneous administration of SZ and nicotinamide, a procedure which prevents pancreatic beta-cell necrosis and induction of diabetes while exposing the nervous system to a possible neurotoxic agent. Selected animals that were given SZ, became diabetic, and subsequently received daily insulin therapy or pancreatic islet transplantation also did not develop axonopathy. Transplantation of pancreatic islets 6 mo after induction of diabetes, a time at which mesenteric axonopathy was well developed, quickly reestablished normoglycemia, and within 3 mo resulted in nearly complete resolution of the neuropathy. Mild chronic diabetes maintained for 5-6 mo failed to produce significant levels of axonopathy.(ABSTRACT TRUNCATED AT 250 WORDS)